Specious
Etymology
From Latin “speciosus,” beautiful or fair to look at, from “species,” outward appearance, from “specere,” to look. It once meant simply good-looking; the meaning soured over centuries into “fair on the surface, false underneath.” The old shine is still what makes it dangerous.
adjective · /SPEE-shuhs/
Superficially convincing but actually wrong or misleading.
What it names
The argument that looks sound until you inspect it — plausibility used as a disguise for a flaw.
Example
The pitch offered a specious guarantee that fell apart the moment anyone read the fine print.
Related idea
A specious argument is plausible but false; a spurious one is fake in its very origin, like a forged source. Specious deceives by looking right; spurious deceives about where it came from.